He has now travelled to England to put the finishing touches to a summer transfer, with the 29-year-old poised to become the first addition of the Unai Emery era at Arsenal.
Sokratis has been a long-standing target for the Gunners and they could be considered to have pulled off quite a coup in securing his signature after interest was shown from a Premier League rival.
The defender’s father, Charalambos Papastathopoulos, told Greek radio station 24/7 on an impending agreement: “There was interest from United but he had to wait until July for them.
“United have a very good relationship with Dortmund, the teams talked but Sokratis chose to go to Arsenal.
“Arsenal had talked two years ago but I don’t know why he didn’t sign.
“He is going to a higher level, the world’s most competitive league and I believe he will do very well.
“Sokratis is in his last year at Dortmund. This was a major reason [for completing the move]
“He is happy, he is in England at the moment and will be doing what he has to do, the typical things, everything will go well, he is happy, he is changing.”
Emery has faced calls to strengthen Arsenal’s defensive unit since succeeding Arsene Wenger at Emirates Stadium.
The Spaniard appears to have heeded that advice, with it possible that a deal for Sokratis could be complemented by the addition of former Juventus full-back Stephan Lichtsteiner.
No deal has been done with the 34-year-old free agent as yet, but positive discussions have been held.